The present invention relates to a gas turbine engine combustor and more particularly to a head part of an annular gas turbine combustor having low cost fuel burner collars to accommodate fuel burners radial-displaceably positioned in passage openings in an upstream end wall of the annular combustor.
Modern gas turbine engines are commonly provided with a generally annular combustor. Usually a wall or bulkhead is provided at the upstream end of the combustor which is suitably apertured to receive a number of fuel burners. The fuel burners are equally spaced around the combustor and direct fuel into the combustor to support combustion therein. The combustor upstream end wall is therefore usually positioned close to the high temperature combustion process taking place within the combustor, making it vulnerable to heat damage.
One way of protecting the upstream end wall of the combustor from the direct effects of the combustion process is to position heat shields on its vulnerable parts. Typically, each heat shield is associated with a corresponding fuel burner and extends both radially towards the radially inner and outer extents of the upstream end wall and circumferentially to abut adjacent heat shields. Each heat shield is spaced apart from the upstream end wall so that a narrow space is defined between them. Cooling air is directed into these spaces in order to provide cooling of the heat shields and so maintain the heat shields and the upstream end wall at acceptably low temperatures.
In practice a fuel burner collar assembly is used to sealingly accommodate the fuel burner radial-displaceably positioned within the passage openings of the upstream end wall of the combustor to permit thermo expansion and contraction of the fuel burner with respect to the upstream end wall of the combustor. Thus, the pressurized air outside the combustor is inhibited from uncontrolled entry into the combustor through the annulus between the fuel burner and the upstream end wall of the combustor.
Conventional fuel burner collar assemblies in the prior art generally have attachment means including for example, brazing, locking sleeves and various interlocking tabs on the collars. One example of fuel collar assemblies is described in U.S. Pat. No. 5,253,471 and 5,271,279, both issued to Richardson on Oct. 19, 1993 and Dec. 21, 1993 respectively. Richardson describes in his both patents, a gas turbine engine annular combustor having a bulkhead at its upstream end which is protected by an annular array of heat shields. An annular seal is located in each bulkhead aperture to receive the fuel burner outlet end, and is provided with a flange which is interposed between an L-shaped cross-section ring and a further ring. The L-shaped ring and the further ring are interconnected by means to support the annular seal, preventing axial movement thereof, but permitting a limited degree of radial movement.
Another example of fuel burner collar assemblies is described in U.S. Pat. No. 5,894,732, issued to Kwan on Apr. 20, 1999. A radially extending flange of the burner sealing part is clamped between the heat shield and the end wall of the combustor. At least one or more annular elements are provided in combination with the burner sealing part and the heat shield to form a relatively complex interlocking system with a series of air supply apertures and chambers to cool the adjacent areas.
A further example of fuel burner assemblies is described in U.S. Pat. No. 5,974,805, issued to Allen on Nov. 2, 1999. Allen describes an arrangement in which a burner miniflare seal is held in position by the heat shield. The heat shield has an aperture, the periphery of which is defined by an axial flange and the burner miniflare seal includes a cylinder portion and a pair of radially extending flanges which slidably engage with the heat shield flange extremities. As a result, the heat shield serves to radially slidably retain the burner miniflare seal. However, an axial flange must be integrated with each heat shield segment which receives the fuel burner, in contrast to conventional heat shields. Furthermore, Allen fails to teach how to place the burner miniflare seal in position within the axial flange of the heat shield if both radial flanges of the seal have a diameter large enough to slidably engage with the heat shield flange extremities, especially when the seal with the pair of radial flanges is an integral single piece part. It would be apparent to those skilled in the art that a multiple piece configuration should be used for the burner miniflare seal in order to position same within the axial flange of the heat shield.
Therefore, there is a need for a simple, one-piece configuration of burner collar without additional securing parts, which will reduce the manufacturing cost thereof.
One object of the present invention is to provide a low cost combustor burner collar assembly which positions a fuel burner in a passage opening in an upstream end wall of a combustor and permits the thermal expansion and contraction thereof with respect to the upstream end wall of the combustor.
Another object of the present invention is to provide a head part of a gas engine combustor wherein a single piece fuel burner collar is radial-displaceably secured to the combustor only by a heat shield attached to the combustor wall.
In accordance with one aspect of the present invention, there is provided a head part of an annular combustor for a gas turbine engine having an upstream end wall with passage openings each of which accommodates a fuel burner. The head part comprises a heat shield detachably secured to a downstream side of the upstream end wall and covering an inner surface thereof, and a burner collar positioned within each of the passage openings and accommodating a corresponding one of the fuel burners. The burner collar has a radial flange with opposed first and second annular radial surfaces. The burner collar is axially restrained directly by the upstream end wall and the heat shield in a manner wherein a radial surface of the downstream side of the upstream end wall abuts the first annular radial surface of the flange, and a radial surface of an upstream side of the heat shield abuts the second annular radial surface of the flange, such that the burner collar is radially displaceable with respect to the upstream end wall.
The burner collar preferably includes an annular cylinder, and the radial flange extends radially and outwardly from the external periphery of the annular cylinder.
In one embodiment of the present invention the burner collar includes an annular cylinder and a skirt portion having an outer diameter smaller than a diameter of the passage opening in the upstream end wall of the combustor. The flange preferably extends radially and outwardly from a downstream end of the annular cylinder and has an outer diameter greater than the diameter of the passage opening. The heat shield preferably has threaded studs which are integrated with the heat shield and extend through openings in the upstream end wall of the combustor. Self-locking nuts are used to engage the respective threaded studs in order to secure the heat shield to the upstream end wall. The heat shield has a configuration such that when the heat shield is secured to the upstream end wall the radial surface of the heat shield is axially spaced a predetermined distance apart from the radial surface of the downstream side of the upstream end wall to form a gap for fittably and radial-displaceably accommodating the flange of the burner collar therein.
In accordance with another aspect of the present invention, there is provided a method for securing a burner collar to a gas turbine engine combustor for accommodating a fuel burner radial-displaceably positioned in a passage opening in an upstream end wall of the combustor. The method comprises a step of axially restraining the burner collar in the passage opening by using a heat shield which is detachably secured to a downstream side of the upstream end wall and covering an inner surface thereof, to directly abut a radial flange of the burner collar against a radial surface of the upstream end wall of the combustor such that the burner collar is radially displaceable with respect to the upstream end wall of the combustor.
In contrast to multi-part assemblies of burner collars in the prior art, the present invention advantageously provides a single piece configuration of a burner collar which needs no additional parts to hold the burner collar in position. Instead, the axial flange of the burner collar is simply clamped between the conventional heat shield and the upstream end wall of the combustor. Therefore, the burner collar can be manufactured economically and the overall weight of the gas turbine engine combustor can be reduced, which is also a desirable advantage especially when the gas turbine engine is used in aircraft.
Other advantages and features of the present invention will be better understood with reference to a preferred embodiment of the present invention described hereinafter.